Micro-devices, or micro-machines, as discussed herein, are devices, often mechanical, electrical, or both, in nature, less than 200 microns in size. Structures and devices of this size and smaller can be built in many ways, such as using MEMS (micro-electro mechanical systems) techniques, which often employ lithography to create microscopic structures (and thereby overlap with integrated circuit manufacture techniques), self-assembly, micro-machining, 3D printing, or any other suitable technique. Note that while an entire micro-device may be up to 200 microns in size, its individual parts may be much smaller. For example, the state of the art in integrated circuit lithography allows features of 22 nm or smaller, imprint lithography allows features smaller than 10 nm, self-assembly allows the creation of structures based on individual molecules, and AFM or SFM-based technologies allow the placement individual atoms. The methods of construction of micro-devices are numerous, and known to those skilled in the art, but for example, U.S. Pat. No. 8,276,211 to Freitas Jr. et al., and US Applications 20130184461, 20130178626, and 20130178627 to Freitas Jr. et al. describe atomically-precise techniques by which such devices could be created, out of diamondoid and other materials, and the contents of these documents is hereby incorporated by reference.
Micro-devices have many potential applications. For example, in the medical field implanted micro-devices could provide high-resolution, real-time measures of many properties. Important solutes could be measured (e.g., glucose, sodium, potassium, calcium, bicarbonate, etc.), as could physical properties such as temperature and pressure. Current examples of macro-scale devices directed at performing similar functions include pill-sized cameras to view the digestive tract as well as implanted glucose and bone growth monitors to aid treatment of diabetes and joint replacements, respectively. The development of micro-devices significantly extends the capabilities of such machines. For example, clinical magnetic resonance imaging (MRI) can move micro-devices containing ferromagnetic particles through blood vessels. (ISHIYAMA, K., SENDOH, M., et al.; “Magnetic micromachines for medical applications.” J. of Magnetism and Magnetic Materials (2002) 242-245: 41-46.; MARTEL, S., MATHIEU, J.-B., et al; “Automatic navigation of an untethered device in the artery of a living animal using a conventional clinical magnetic resonance imaging system.” Applied Physics Letters (2007) 90.; OLAMAEI, N., CHERIET, F., et al.; “MRI visualization of a single 15 μm navigable imaging agent and future microrobot.” Proc. of the 2010 IEEE Conf. on Engineering in Medicine and Biology Society (2010); 4355-4358.)
Other demonstrated micro-devices use flagellar motors to move through fluids, and offer the possibility of minimally invasive microsurgeries in parts of the body beyond the reach of existing catheter technology. (BEHKAM, B. and SITTI, M.; “Bacterial Flagella-Based Propulsion and On/Off Motion Control of Microscale Objects.” Applied Physics Letters (2007) 90.; FERNANDES, R. and GRACIAS, D.; “Toward a Miniaturized Mechanical Surgeon.” Materials Today (2009) 12(10): 14-20.). The uses for such devices are numerous and extend beyond the field of medicine to uses such as basic research and industrial applications. Note that while exemplary uses are described herein, others will be apparent to those skilled in the art. It should be recognized that the value in the present invention resides in the general principles provided for communicating, powering, and shaping and creating acoustic fields using micro-devices of many different types, in many different environments, not just those mentioned or shown in the embodiments.
Providing power to micro-devices is a challenge. For example, power from batteries would be limited by their small size and power harvested from the environment is limited by available energy sources and the complexity of manufacturing power generating components at small sizes. Other techniques, such as inductive powering and other forms of wireless power transmission pose other problems in light of factors such as the frequencies needed to efficiently couple to micro-devices, attenuation, and for some applications, safety.
Communication poses a challenge for micro-devices. Small overall device size limits antenna size, which makes selection of wavelengths which can be adequately coupled to a micro transceiver problematic. Further, the optimal modes of communication of a micro-device with a macro-scale transceiver may differ from the optimal modes of communication between micro-devices. Communication between micro-devices can address several problems. For example, such communications could enable micro-devices to coordinate their activities, thereby providing a wider range of capabilities than having each micro-device act independently of others. For instance, nearby micro-devices could compare their measurements to improve accuracy by averaging noise, determine gradients or identify anomalous behaviors such as the failure of a device. Such communication could also allow the micro-devices to combine their measurements into compressed summaries, thereby reducing the amount of information necessary to communicate to an external transceiver. And, communication between micro-devices enables data to be sent to the micro-device closest to, or in best communication with, an external transceiver.
The small size of the micro-devices is not the only challenge to providing power and communication. Micro-devices may operate within environments which raise additional challenges. For example, in the body, tissues, including blood, different organ tissues, and bone, may have physical properties that are not well-characterized at the small sizes relevant to micro-devices and such properties can vary over short distances. The tissue properties may affect transceiver and micro-device design and performance due, for example, to its attenuation characteristics.
Acoustics are one approach to coupling power and data transmission to micro-devices. Sound is readily transmitted through many materials and is easily produced by micro-devices. Ultrasound has been used to communicate with conventional, large-scale implants, and micro-devices can use piezoelectric materials, among other techniques, to produce sound. However, the small size of micro-devices makes them inefficient at converting vibration into sound waves at the frequencies commonly used by larger devices. Micro-devices are more efficient at generating higher frequency sounds. However, many environments including water and biological tissue significantly attenuate high-frequency sound. Even air substantially attenuates sound at high enough frequencies. Compensating for inefficiency or attenuation by using increased power may be impractical due to power limitations. And, in biological settings, even if sufficient power were available, increased power could lead to localized tissue damage due to intense power flux at the surface of the micro-device. Overcoming these problems requires creating a sound field adapted for transmission through various environments such as various gases, water or other fluids, blood, tissue, industrial chemicals or waste, or other environments, through suitable choices of operating frequencies and other parameters. Different choices may be required for sending sound from micro-devices to each other, from a micro-device to an external transceiver, and from an external transceiver to the micro-device. Aggregate sound fields, discussed herein in more detail, add to the complexity of these problems.
Acoustics, in the form of ultrasound, has been used for imaging, cleaning and agitation, industrial and biological measurement and testing, the enhancement of drug delivery (see U.S. Pat. No. 7,985,184 to Sarvazyan on Jul. 26, 2011 for “Ultrasound-assisted drug-delivery method and system based on time reversal acoustics”) as an adjunct to antibiotic therapy (and other uses related to cell permeability), for welding, for USID (ultrasound identification), and more. Micro-devices capable of generating ultrasound have the potential to provide similar functions, if the attendant problems with small device size can be overcome.
U.S. Pat. No. 7,570,998 to Zhang et al. on Aug. 4, 2009 for “Acoustic communication transducer in implantable medical device header,” teaches an implantable medical device containing an ultrasonic transducer. Communication between the device and an implanted sensor occurs using frequencies in the 10-100 kHz range. These frequencies are suitable for conventional devices, but not micro-scale devices.
U.S. Pat. No. 7,945,064 to O'Brien Jr. et al. on May 17, 2011 for “Intrabody communication with ultrasound,” teaches the use of acoustics as an alternative to RF transmission. This describes macro-scale ultrasonic transducers using part of body as a communication channel at frequencies between 100 kHz and 10 MHz. This reference does not teach the use of micro-devices, and the frequencies are generally too low to efficiently couple to micro-devices.
U.S. Pat. No. 8,040,020 to Martin et al. on Oct. 18, 2011 for “Encapsulated active transducer and method of fabricating the same” teaches MEMS-based ultrasound generators. Specific applications (e.g., communication within tissue) are not discussed.
U.S. Pat. No. 8,088,067 to Vortman et al. on Jan. 3, 2012 for “Tissue aberration corrections in ultrasound therapy,” teaches adjusting ultrasound for tissue inhomogeneities at larger scales for improved focus. The size scales, and attendant challenges, are different than the present invention.
Theoretical studies of communication with and among sub-millimeter implanted devices, have been published (FREITAS, R., Nanomedicine, Volume I: Basic Capabilities, Chapter 7(1999) Landes Bioscience.; and HOGG, T. and FREITAS, R.; “Acoustic communication for medical nanorobots.” (2012) Nano Communication Networks.), by the inventors and upon which this application is based and which is herein incorporated by reference). However, these studies do not address all of the challenges or details involved in micro-scale communication, power, or aggregation.
While some differences between the invention and the literature are listed above, a more general observation should be made: The literature is not directed to surmounting the practical problems inherent in transmitting, receiving and coordinating sound at small scales and distances in real-world environments such as limitations in available power, sound coupling to micro-devices in general, sound coupling to micro-devices of various sizes, acoustic attenuation in various environments (e.g., air, water, various biological tissues, industrial effluent), efficient acoustic wave generation by micro-devices, noise, communication rates, near field versus far field considerations, safety, choice of frequencies, sound reflection or scattering, and aggregation of sound fields and micro-devices.